Implantable medical lead with biased electrode

ABSTRACT

This disclosure describes implantable medical leads that include a lead body and an electrode. A width of the electrode as measured along a longitudinal direction of the lead varies about the perimeter of the lead. The uneven width of the electrode may bias a stimulation field in a particular direction, e.g., a radial or transverse direction relative to the longitudinal axis of the lead. Electrodes with an uneven width may be useful for controlling the direction of propagation of the stimulation field in order to, for example, avoid phrenic nerve stimulation during LV pacing or neck muscle stimulation during vagal neurostimulation.

TECHNICAL FIELD

The present disclosure relates to medical devices, more particularly toimplantable medical leads.

BACKGROUND

In the medical field, implantable leads are used with a wide variety ofmedical devices. For example, implantable leads are used withimplantable cardiac pacemakers that provide therapeutic stimulation tothe heart by delivering pacing, cardioversion or defibrillation pulsesvia the leads. Implantable cardiac pacemakers deliver such pulses viaelectrodes disposed on the leads, e.g., near distal ends of the leads.Implantable medical leads may be configured to allow electrodes to bepositioned at desired cardiac locations so that the pacemaker candeliver pulses to the desired locations.

Implantable medical leads are also used with other types of stimulatorsto provide, as examples, neurostimulation, muscular stimulation, orgastric stimulation to target patient tissue locations via electrodes onthe leads and located within or proximate to the target tissue. As oneexample, implantable medical leads may be positioned proximate to thevagal nerve for delivery of neurostimulation to the vagal nerve.Additionally, implantable medical leads may be used by medical devicesfor patient sensing and, in some cases, for both sensing andstimulation. For example, electrodes on implantable medical leads maydetect electrical signals within a patient, such as anelectrocardiogram, in addition to delivering electrical stimulation.

For delivery of cardiac pacing pulses to the left ventricle (LV), animplantable medical lead is typically placed through the coronary sinusand into a coronary vein. However, when located in the coronary sinus ora coronary vein, an LV lead may also be located near the phrenic nerve.Phrenic nerve stimulation is generally undesirable during LV pacingtherapy. In some instances, the implantable lead may need to bespecifically positioned to avoid phrenic nerve stimulation during LVpacing therapy, which may result in placing the electrodes of the LVlead at a non-optimal site for LV pacing.

In some cases, implantable medical leads with ring electrodes are usedas an alternative to cuff electrodes for delivery of neurostimulation tothe vagal nerve. However, when located near the vagal nerve, theimplantable medical lead may also be located near neck muscles.Stimulation of neck muscles is generally undesirable during therapeuticvagal stimulation.

SUMMARY OF THE DISCLOSURE

In general, the present disclosure is directed toward controlling thedirection of a stimulation field. An implantable medical lead mayinclude at least one ring or ring-like electrode with an uneven width.For example, the width of the ring electrode as measured along thelongitudinal direction of the lead may vary about the perimeter of thelead.

The uneven width of the electrode may bias a stimulation field in aparticular direction, e.g., a radial or transverse direction relative tothe longitudinal axis of the lead. For example, rather than distributingequally about the perimeter of the lead, as would typically occur whenstimulation is delivered via a ring electrode with a substantially evenwidth about the perimeter of the lead, the stimulation field may bebiased toward the portion or “side” of the lead body where the electrodehas an increased surface area. Electrodes with an uneven width, referredto herein as biased electrodes, may be useful for controlling thedirection of propagation of the stimulation field in order to, forexample, avoid phrenic nerve stimulation during LV pacing or neck musclestimulation during vagal neurostimulation.

In one embodiment, an implantable medical lead comprises a lead bodyinsulation and an electrode, wherein a width of the electrode asmeasured along a longitudinal direction of the lead varies about aperimeter of the lead.

In another embodiment, a system comprises an implantable medical lead,wherein the lead comprises a lead body insulation and an electrode,wherein a width of the electrode as measured along a longitudinaldirection of the lead varies about a perimeter of the lead. The systemfurther comprises a medical device that delivers electrical stimulationvia the electrode.

In yet another embodiment, a method of implanting an implantable medicallead comprises inserting the lead into a patient. The lead includes leadbody insulation, and an electrode positioned on the perimeter of leadbody insulation, wherein a width of the electrode as measured along alongitudinal direction of the lead varies about a perimeter of the lead.The method of implanting the implantable medical lead further comprisesvisualizing an orientation of the lead within the patient; adjusting theorientation of the lead based on the visualization; and deliveringtherapy to the patient using the electrode.

In another embodiment, a method of manufacturing an implantable medicallead comprises forming a lead body with at least one conductor; andcoupling an electrode to the conductor. A width of the electrode asmeasured along a longitudinal direction of the lead varies about aperimeter of the lead after coupling the electrode to the conductor.

A method comprises implanting an electrical stimulation lead within apatient. The lead comprises a lead body, and an electrode, wherein awidth of the electrode as measured along a longitudinal direction of thelead varies about a perimeter of the lead. The method further comprisesdelivering stimulation therapy to a tissue within the patient using theelectrode.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andbenefits of the present disclosure will be apparent from the descriptionand drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example implantablemedical device system.

FIG. 2A is a side view of a distal end of an embodiment of animplantable medical lead including a biased ring electrode.

FIG. 2B is a cross-sectional view of a distal end of the implantablemedical lead of FIG. 2A.

FIG. 3 is a side view of a distal end of another embodiment of animplantable medical lead including two biased ring electrodes that arecomplimentary along an interface between the two electrodes.

FIG. 4 is a side view of a distal end of another embodiment of animplantable medical lead including three biased ring electrodes andillustrating electrical conductors within the lead body.

FIG. 5 is a flowchart illustrating a method of using an implantablemedical lead with a biased electrode.

FIG. 6 is a flowchart illustrating a method of manufacturing animplantable medical lead with a biased electrode.

DETAILED DESCRIPTION

In general, the present disclosure is directed toward controlling thedirection of propagation of a stimulation field. An implantable medicallead may include at least one biased ring electrode. A width of thebiased ring electrode in a longitudinal direction of the lead variesabout the perimeter of the lead. The biased electrode may aid indirecting a stimulation field in a particular transverse or radialdirection. For example, rather than distributing equally about theperimeter of the lead, the stimulation field may be biased to theportion or side of the lead where the biased electrode has an increasedsurface area. Controlling the direction of the stimulation field may beuseful, for example, to avoid phrenic nerve stimulation during LV pacingor neck muscle stimulation during vagal neurostimulation.

While the description primarily refers to implantable medical leads andimplantable medical devices, such as pacemakers andpacemaker-cardioverter-defibrillators, that deliver stimulation therapyto a patient's heart, the features of the leads described herein areuseful in other types of medical device systems, which may include othertypes of implantable medical leads and implantable medical devices. Forexample, leads including the features described herein may be used insystems with medical devices that deliver neurostimulation to the vagalnerve. As other examples, leads including the features described hereinmay be used in systems that deliver other types of neurostimulationtherapy (e.g., spinal cord stimulation or deep brain stimulation),stimulation of one or more muscles or muscle groups, stimulation of oneor more organs, such as gastric stimulation, stimulation concomitant togene therapy, and, in general, stimulation of any tissue of a patient.

Furthermore, although described herein as being coupled to IMDs,implantable medical leads of according to the present disclosure mayalso be percutaneously coupled to an external medical device for deliverof electrical stimulation to target locations within the patient.Additionally, the disclosure is not limited to embodiments that deliverelectrical stimulation to a patient, and includes embodiments in whichelectrical signals or other physiological parameters are sensed via animplantable medical lead with an electrode having an uneven width aboutthe perimeter of the lead.

For example, for effective cardiac pacing, stimulation therapy can be ofadequate energy for a given location to cause depolarization of themyocardium. Sensing a physiological parameter of the patient may be usedto verify that pacing therapy has captured the heart, i.e., initiated adesired response to the therapy such as, for example, providing pacing,resynchronization, defibrillation and/or cardioversion. Such sensing mayinclude sensing an evoked R-wave or P-wave after delivery of pacingtherapy, sensing for the absence of an intrinsic R-wave or P-wave priorto delivering pacing therapy, or detecting a conducted depolarization inan adjacent heart chamber.

These and other physiological parameters may be sensed using electrodesthat may be also used to deliver stimulation therapy. For example, asystem may sense physiological parameters using the same electrodes usedfor providing stimulation therapy or electrodes that are not used forstimulation therapy. As with stimulation therapy, selecting whichelectrode(s) are used for sensing physiological parameters of a patientmay alter the signal quality of the sensing techniques. For this reason,sensing techniques may include one or more algorithms to determine thesuitability of each electrode or electrode combination in thestimulation therapy system for sensing one or more physiologicalparameters. Sensing physiological parameters may also be accomplishedusing electrode or sensors that are separate from the stimulationelectrodes, e.g., electrodes capable of delivering stimulation therapy,but not selected to deliver the stimulation therapy that is actuallybeing delivered to the patient.

Accordingly, a biased electrode having an uneven width about theperimeter of the lead may be selected used, for example, for delivery ofelectrical stimulation, sensing electrical signals, such as anelectrocardiogram for the reasons mentioned above, impedancemeasurements, or uses known for implanted electrodes in the art. Abiased electrode can bias the electric field relative to the lead body.For example, allowing pacing of the left ventricle while reducing nervestimulation such as Phrenic nerve stimulation. Additionally, targetingnerve stimulation such as the vagus nerve while limiting skeletal musclestimulation is also achieved through use of a biased electrode.

In addition, while the examples shown in the figures include leadscoupled at their proximal ends to a stimulation therapy controller,e.g., implantable medical device, located remotely from the electrodes,other configurations are also possible and contemplated. In someexamples, a lead comprises a portion of a housing, or a member coupledto a housing, of stimulation generator located proximate to or at thestimulation site, e.g., a microstimulator. In other examples, a leadcomprises a member at stimulation site that is wirelessly coupled to animplanted or external stimulation controller or generator. For thisreason, as referred to herein, the term of a “lead” includes anystructure having one or more stimulation electrodes disposed on itssurface.

FIG. 1 is a conceptual diagram illustrating an example implantablemedical system 10 comprising implantable medical device (IMD) 12, andimplantable medical leads 14, 16 electrically coupled to IMD 12. In theembodiment shown in FIG. 1, system 10 is implanted to deliverstimulation therapy to heart 5 of patient 18. Patient 18 ordinarily, butnot necessarily, will be a human patient.

In the embodiment shown in FIG. 1, IMD 12 is an implantable cardiacpacemaker, cardioverter, defibrillator, orpacemaker-cardioverter-defibrillator (PCD), that generates therapeuticelectrical stimulation for pacing, cardioversion or defibrillation,which may take the form of pulses or continuous time signals. Leads 14,16 each include at least one electrode that are each positioned within(e.g., intravenously) or proximate to heart 5 (e.g., an epicedial lead)in order to deliver the therapeutic electrical stimulation from IMD 12to heart 5. In some embodiments, at least one of leads 14, 16 mayprovide stimulation to heart 5 without contacting heart 5, e.g., atleast one of leads 14, 16 may include a subcutaneous electrode. Theelectrodes may be disposed proximate to the distal ends of leads 14, 16.

FIG. 2A is a side view of a distal end of an embodiment of a lead 20,which may, for example, correspond to either of leads 14, 16 of FIG. 1.Lead 20 includes a lead body 22 extending from a proximal end (notshown) coupled to an IMD (e.g., IMD 12 of FIG. 1) to a distal endincluding electrodes 24 and 26. Lead body 22 includes one or moreelongated conductors (not shown), one or more electrodes 24, 26, and oneor more elongated insulative bodies. The one or more elongatedconductors (not shown) covered or surrounded by one or more elongatedinsulative bodies. The electrodes 24, 26 are coupled to the conductorsand are not covered by the insulative body or covering. Allowingelectrodes 24, 26 to be exposed to tissue of the patient allows data tobe sensed from the tissue and/or therapy delivered to the patient.Exemplary conductors such as cabled conductors or wires can compriseplatinum, platinum alloys, titanium, titanium alloys, tantalum, tantalumalloys, cobalt alloys (e.g. MP35N, a nickel-cobalt alloy etc.), copperalloys, silver alloys, gold, silver, stainless steel, magnesium-nickelalloys or other suitable materials. Lead body 22 may be sized based on atarget stimulation site within a patient (e.g., patient 18 of FIG. 1)and a path through the patient that lead 20 can traverse in order toplace electrodes 24 and 26 at the target stimulation site. Electrodes 24and 26 may also be sized based on the size of lead 20 and a targetstimulation site within the patient.

Lead body 22 along with electrodes 24 and 26 may be, for example, sizedto pass through and/or fit in the coronary sinus or a small and/or largecoronary vein. Accordingly, lead 20 may correspond to left-ventricular(LV) lead 14 illustrated in FIG. 1, and be used for LV pacing and/orsensing. As another example, for vagal stimulation therapy lead body 22and electrodes 24 and 26 may be sized to fit within the internal jugularvein of a patient. Lead 20 may also include a monolithic controlledrelease device (MCRD) 28 containing a steroid. In the embodimentillustrated in FIG. 2A, MCRD 28 is positioned between electrodes 24 and26.

In the illustrated embodiment, electrode 26 is a tip electrode locatedat the distal tip of lead 20. In some embodiments, electrode 26 may beformed to provide fixation for lead 20, e.g., may be formed as a helixor screw-like electrode for fixation within tissue of the patient.Electrode 26 may be porous or otherwise allow passage of a steroid orother material from MCRD 28 to patient tissue.

In some embodiments, electrode 26 may be a ring electrode with asubstantially circular cross-section. In other embodiments, electrode 26may comprise a plurality of segmented or partial ring electrodes, eachof the electrode segments extending along an arc less than 360 degrees(e.g., 90-120 degrees) about the circumference or perimeter of lead 20.Segmented or partial ring electrodes may be useful for providing anelectrical stimulation field in a particular propagation directionand/or targeting a particular stimulation site by selective activationof electrodes most proximate to the site, or facing in the desiredpropagation direction.

As shown in FIG. 2A, electrode 24 is a biased ring electrode. The widthof biased ring electrode 24 as measured along the longitudinal axis 30of the lead 20, i.e., a longitudinal direction, varies about theperimeter, e.g., circumference, of the lead 20. More specifically, thewidth of ring electrode 24 varies around a circumference of lead 20 suchthat the surface area of ring electrode 24 is greater on one side orportion of lead 20, e.g., within a particular radial section of lead 20.

In the embodiment illustrated in FIG. 2A, a first radial portion of ringelectrode 24 has a width W1, and a second radial portion of ringelectrode 24 has a width W2. Width W2 is greater than width W1 such thatthe portion, e.g., radial section, of electrode 24 with increased widthW2 forms a protrusion in the direction of longitudinal axis 30. In someembodiments, W2 is about 2 mm to 20 mm larger than width W1. As anotherexample, W2 may be about 1 to 2000 percent larger than width W1. In yetanother embodiment, W2 may be about 25 percent larger than width W1. Inyet another embodiment, W2 may be about 30 percent larger than width W1.In yet another embodiment, W2 may be about 40 percent larger than widthW1. In yet another embodiment, W2 may be about 50 percent larger thanwidth W1. In yet another embodiment, W2 may be about 60 percent largerthan width W1. In yet another embodiment, W2 may be about 70 percentlarger than width W1. In yet another embodiment, W2 may be about 80percent larger than width W1. In yet another embodiment, W2 may be about90 percent larger than width W1. In yet another embodiment, W2 may beabout 100 percent larger than width W1. In yet another embodiment, W2may be about 200 percent larger than width W1. In yet anotherembodiment, W2 may be about 300 percent larger than width W1. In yetanother embodiment, W2 may be about 400 percent larger than width W1. Inyet another embodiment, W2 may be about 500 percent larger than widthW1. In yet another embodiment, W2 may be about 600 percent larger thanwidth W1. In yet another embodiment, W2 may be about 700 percent largerthan width W1. In yet another embodiment, W2 may be about 800 percentlarger than width W1. In yet another embodiment, W2 may be about 900percent larger than width W1. In yet another embodiment, W2 may be about1000 percent larger than width W1. The relationship between widths W1and W2 may be configured to control the direction of propagation of astimulation field generated using biased electrode 24.

When biased electrode 24 is activated (i.e., as a cathode or an anode)to deliver stimulation, the resulting stimulation field is biasedtowards the side or radial portion of biased electrode 24 having agreater surface area, e.g., propagates a greater distance outward fromthe lead body in a radial, transverse or cross-sectional direction. Incontrast, a stimulation field from a ring electrode having asubstantially constant width about the perimeter of a lead body issubstantially equally distributed about the perimeter of the lead 20,i.e., propagates a substantially constant transverse or radial distancefrom the lead.

A biased ring electrode can be useful in directing a stimulation fieldtoward a target tissue site and/or away from an undesirable tissue site.As one example, a directional stimulation field may be particularlyuseful in left ventricle (LV) pacing applications. The biased ringelectrode may allow the field to be directed toward the myocardium andaway from the phrenic nerve.

As another example, a biased ring electrode may be useful in stimulationof the vagus nerve. Stimulation of the vagus nerve may be performed to,for example, decrease or otherwise regulate heart rate. The vagus nerveis positioned proximate to muscles of the neck, which may inadvertentlybe stimulated along with the vagus nerve. Controlling the direction ofthe stimulation field may aid in preventing stimulation of the neckmuscles.

As another example, a directional electrical field may be useful inatrial stimulation, where it may be desirable to avoid stimulatingspecific ischemic tissue regions. In general, a biased ring electrodemay be beneficial in any application where controlling the direction ofpropagation of the stimulation field, e.g., in a transverse, radial orcross-sectional direction, is desirable.

Electrode 24 may be activated as a cathode or anode, with electrode 26or another electrode, e.g., an electrode located on a housing of an IMD,such as IMD 12, activated with the opposite polarity. Furthermore,although electrode 24 has an uneven width in the illustrated embodiment,either or both of electrodes 24 and 26 may have an uneven width invarious embodiments. Accordingly, in some embodiments, a tip electrodemay be a biased electrode and, in various embodiments, a biasedelectrode may act as either an anode or cathode for delivery ofstimulation to a patient.

Additionally, the disclosure is not limited to embodiments in which thebiased electrode has the shape or form illustrated by electrode 24 inFIG. 2A. A biased electrode may include a portion, e.g., radial section,that forms a protrusion in the direction of longitudinal axis 30, asillustrated by electrode 24 in FIG. 2A. The remainder of the biasedelectrode may, but need not necessarily, take the form of a ringelectrode with a substantially constant width, as illustrated byelectrode 24 in FIG. 2A. However, in other embodiments, a biasedelectrode may have any shape or form. For example, one or both of theedges of the electrode may define a regular, irregular, or random,curvilinear or geometric line around the perimeter of lead body, suchthat the width of the electrode in the direction of longitudinal axis 30varies around the perimeter.

At least a portion of lead 20, such as electrodes 24 and 26 or aseparate marker loaded in or formed on lead body 22, may include aradio-opaque material that is detectable by imaging techniques, such asfluoroscopic imaging or x-ray imaging. For example, electrodes 24 and 26may be made of platinum or another material detectable by imagingtechniques. This feature may be helpful for maneuvering lead 20 relativeto a target site within the body. Radio-opaque markers, as well as othertypes of markers, such as other types of radiographic and/or visiblemarkers, may also be employed to assist a clinician during theintroduction and withdrawal of lead 20 from a patient. Markersidentifying a portion or side of a lead in which an electrode has agreater width (and, accordingly, greater surface area) may beparticularly helpful. Since the electrodes rotate with the lead body, aclinician may rotate the lead and the electric field to stimulate adesire tissue, i.e., rotate the lead such that the portion with greaterelectrode surface area faces target tissue and/or is directed away fromtissue to which delivery of stimulation is undesirable. Markers may helpguide the rotation to control the direction of propagation of thestimulation field once the lead is implanted.

In the embodiment illustrated in FIG. 2A, electrodes 24 and 26 may becoupled to an IMD (e.g., IMD 12 of FIG. 1) using an industry standard-1(IS-1) connector, which allows the connection of up to two independentlyactivatable channels. More specifically, electrical conductors (notshown) may couple electrodes 24 and 26 to an IMD (e.g., IMD 12 ofFIG. 1) via an IS-1 connector. Some commercially available IMDs areconfigured according to the IS-1 standard. An IS-1 compatible lead maybe easily coupled to these commercially available devices. In otherembodiments, lead 20 may include any configuration, type, and number ofelectrodes 24 and 26 and is not limited to the embodiment illustrated inFIG. 2A.

FIG. 2B is a cross-sectional view of a distal end of implantable medicallead 20 illustrating radial section 32. Radial section 32 corresponds tothe portion of electrode 24 with increased width W2 in the direction oflongitudinal axis 30 as illustrated in FIG. 2A. Radial section 32extends around a portion of the perimeter of lead 20. Due to theincreased width W2 of electrode 24 at radial section 32, electrode 24also has an increased surface area at radial section 32. When biasedelectrode 24 is activated (i.e., as a cathode or an anode) to deliverstimulation, the resulting stimulation field is biased towards radialsection 32 of biased electrode 24, i.e., the resulting stimulation fieldpropagates a greater distance outward from lead 20 in a radial,transverse or cross-sectional direction. Outlines 34A and 34B representthe outer boundaries of example stimulation fields that may be generatedwhen biased electrode 24 is activated to deliver stimulation andillustrate how the stimulation fields propagate a greater distanceoutward from lead 20 proximate to radial section 32 compared to theother portions of the perimeter of lead 20. The actual stimulation fieldis dependent not only on the shape of biased electrode 24, but alsoother factors such as the amplitude of stimulation therapy, the locationand configuration of addition electrodes such as electrode 26, as wellas the impedance of patient tissue or other substances adjacent to thestimulation field. As referred to herein, an amplitude of stimulationtherapy may be characterized as a magnitude of a time varying waveform.For example, an amplitude of stimulation therapy may be measured interms of voltage (volts), current (ampere), or electric field(volts/meter). Typically, amplitude is expressed in terms of a peak,peak to peak, or root mean squared (rms) value.

FIG. 3 is a side view of a distal end of another embodiment of animplantable medical lead 40. Lead 40 is similar to lead 20 of FIGS. 2Aand 2B but, as described in further detail below, includes threeelectrodes 44A, 44B, and 46. Lead 40 includes a lead body 42 thatextends from a proximal end (not shown) coupled to an IMD (e.g., IMD 12of FIG. 1) to a distal end that includes electrodes 44A, 44B, and 46.Electrode 46 may take any of the forms described above with respect toelectrode 26 and FIG. 2A. Furthermore, lead 40 may include an MCRD 50that may substantially similar to and provides substantially the samefunctionality as MCRD 28 described above with respect to FIG. 2A.

In the embodiment illustrated in FIG. 3, lead body 42 includes twobiased ring electrodes 44A and 44B. A width of each of electrode 44A and44B as measured along the direction of longitudinal axis 52 of the leadbody 42, i.e., a longitudinal direction, varies around a perimeter oflead 40. In the embodiment illustrated in FIG. 3, electrodes 44A and 44Bare substantially complimentary. In particular, as shown in FIG. 3, whenthe width of one of electrodes 44A and 44B in the longitudinal directionchanges, the width of the other of electrodes 44A and 44B also changeswith a substantially equal but opposite magnitude. Thus, in theembodiment illustrated in FIG. 3, the sum of the widths of electrodes44A and 44B may be substantially about the same at any circumferentialposition of lead 40. Substantially about the same, in one embodiment,means that the sum of the widths of electrodes 44A and 44B are within 20percent of one another. Electrodes 44A and 44B are also complimentary inthe sense that the lines (curvilinear in the illustrated example) aroundthe perimeter of lead 40 formed by the adjacent edges of the electrodes,e.g., the edges where electrodes 44A and 44B interface, aresubstantially similar. Insulative material 48 separates electrodes 44Aand 44B to electrically isolate electrodes 44A and 44B. For example,insulative material 48 may comprise polyurethane, silicone, andfluoropolymers such as tetrafluroethylene (ETFE), polytetrafluroethylene(PTFE), and/or expanded PTFE (i.e. porous ePTFE, nonporous ePTFE).

The surface area and shape of each of electrodes 44A, 44B, and 46 may beselected based on the desired stimulation field. For example, thesurface area and shape of each of electrodes 44A, 44B, and 46 may beselected to aid in selectively exciting a tissue based on thegeometrical proximity to lead 40 and/or the field gradient to which thetarget tissue responds. Any of electrodes 44A, 44B, and 46 may beconfigured as a cathode or an anode to aid in creating the desiredstimulation field. As one example, electrode 44A may be configured as ananode, and electrode 44B may be configured as a cathode to create adesired stimulation field. As another example, electrode 46 may beactivated as an anode or cathode, and one of electrodes 44A and 44B maybe activated with the opposite polarity. Which of electrodes 44A and 44Bis selected may be based on a desired direction of propagation or shapeof the stimulation field.

FIG. 4 is a side view of a distal end of an embodiment of an implantablemedical lead 60. Lead 60 includes a lead body 62 that extends from aproximal end (not shown) coupled to an IMD (e.g., IMD 12 of FIG. 1) to adistal end that includes electrodes 64A-64C and 66. Lead body 62 may besized to fit in a small and/or large coronary vein. Accordingly,electrodes 64A-64C and 66 may also be sized based on the size of leadbody 62 and a target stimulation site within a patient (e.g., patient 18of FIG. 1). In other embodiments, lead 60 may include any configuration,type, and number of electrodes 64A-64C and 66 and is not limited to theembodiment illustrated in FIG. 4.

In the embodiment illustrated in FIG. 4, lead 60 includes biased ringelectrode 66 at its distal tip and three biased ring electrodes 64A-64Caxially displaced from biased ring electrode 66. A width of each ofelectrode 64A-64C and 66 in the longitudinal direction, i.e., in thedirection along a longitudinal axis (not shown) of lead 60, variesaround a circumference or perimeter of lead 60. For example, electrode64 includes an increased width and surface area at one portion of thecircumference of lead 60.

Electrodes 64A and 64B are substantially complimentary. For example,when one of electrodes 64A and 64B changes shape along the interfacebetween electrodes 64A and 64B, the other of electrodes 64A and 64B alsochanges shape in an opposite direction but with an equal magnitude.Similarly, electrodes 64B and 64C are also substantially complimentary.In the embodiment illustrated in FIG. 4, the sum of the widths ofelectrodes 64A-64C may be substantially the same at any circumferentialposition of lead 60. Insulative material 68 separates electrodes 64A and64B and also separates electrodes 64B and 64C. Insulative material 68may aid in electrically isolating electrodes 64A-64C. For example,insulative material 68 may comprise polyurethane, silicone, andfluoropolymers such as tetrafluroethylene (ETFE), polytetrafluroethylene(PTFE), and/or expanded PTFE (i.e. porous ePTFE, nonporous ePTFE).

The surface area and shape of each of electrodes 64A-64C and 66 may beselected based on the desired stimulation field. For example, thesurface area and shape of each of electrodes 64A-64C and 66 may beselected to target a tissue based on the geometrical proximity to lead60 and/or the field gradient to which the target tissue responds. Any ofelectrodes 64A-64C and 66 may be configured as a cathode or an anode toaid in creating the desired stimulation field. As one example,electrodes 64A and 64C may be configured as anodes and electrode 64B maybe configured as a cathode to create a desired stimulation field. Asanother example, electrode 66 may be activated as an anode or cathode,and one of electrodes 64A-64C may be activated with the oppositepolarity to create a desired stimulation field, with the selection ofwhich of electrodes 64A-64C is activated being based on the desiredstimulation field, the orientation of lead 60 and electrodes 64A-64Crelative to target patient tissue for stimulation or tissue to beavoided, or the like.

Lead 60 also includes conductors 70A-70C and 72 electrically coupled toelectrodes 64A-64C and 66, respectively. In the illustrated embodiment,conductors 70A-70C are coiled along the length of lead body 62, andconductor 72 lays axial to conductors 70A-70C. Although not illustratedin FIG. 4, conductor 72 may also be coiled, and may or may not bebraided with conductors 70A-70C. In the embodiment illustrated in FIG.4, each of conductors 70A-70C and 72 is electrically coupled to a singleone of electrodes 64A-64C and 66, respectively. In this manner, each ofelectrodes 64A-64C and 66 may be independently activated. Electrodes64A-64C and 66 may be coupled to an IMD (e.g., IMD 12 of FIG. 1) using,for example, an industry standard-4 (IS-4), which allows the connectionof up to four independently activatable channels. More specifically,conductors 70A-70C and 72 may couple electrodes 64A-64C and 66 to an IMD(e.g., IMD 12 of FIG. 1) via an IS-4 connector.

The configuration, type, and number of electrical conductors 70A-70C and72 is not limited to the embodiment illustrated in FIG. 4 and, in otherembodiments, lead 60 may include any configuration, type, and number ofconductors. As one example, in some embodiments, each of conductors70A-70C and 72 may be coiled conductors. Additionally or alternatively,one conductor may be electrically coupled to two or more electrodes.Additionally, each of leads 12, 14, 20 and 40 may include conductors toelectrically couple its electrodes at the distal end of its lead body toan IMD (e.g., IMD 12 of FIG. 1) coupled to the proximal end of its leadbody. In another embodiment, a lead including multiple electrodes mayinclude a multiplexer or other switching device such that the lead bodymay include fewer conductors than electrodes while allowing each of theelectrodes to be individually selectable.

FIG. 5 is a flowchart illustrating a method of using an implantablemedical lead with a biased electrode. A lead comprising a biasedelectrode is inserted into a patient (80) and its distal end is guidedto a target tissue site. The target tissue site may be, for example, themyocardium of the heart, near the phrenic nerve, the vagus nerve, or anyother location where controlling the direction of propagation of thestimulation field is desirable.

Once the distal end of the lead is positioned at the target tissue site,an orientation of the lead is visualized (82), and the orientation isadjusted based on the visualization (84). As described previously,radio-opaque markers, as well as other types of markers, such as othertypes of radiographic and/or visible markers, may also be employed toassist a clinician during the introduction and withdrawal of a leadcomprising a biased electrode from a patient. Markers identifying aportion or side of a lead in which an electrode has a greater width(and, accordingly, greater surface area) may be particularly helpful.Since the electrodes rotate with the lead body, a clinician may rotatethe lead and the electric field to stimulate a desire tissue, i.e.,rotate the lead such that the portion with greater electrode surfacearea faces target tissue and/or is directed away from tissue to whichdelivery of stimulation is undesirable. Markers may help guide therotation to control the direction of propagation of the stimulationfield once the lead is implanted.

Once the lead is properly orientated, therapy is delivered to thepatient using one or more electrodes of the lead (86). For example, amedical device coupled to the implantable medical lead may activate theelectrode to deliver therapy to the patient. In some embodiments, themedical device may deliver one or more electrical test signals to thepatient to verify that the lead is properly orientated prior toinitiating therapy delivery.

FIG. 6 is a flowchart illustrating a method of manufacturing animplantable medical lead with a biased electrode. The method comprisesforming a lead body (90) and coupling the biased electrode to the leadbody (92). In some embodiments, the lead body is formed using extrusion,and the biased electrode may be positioned on the lead body such that anouter surface of the biased electrode is substantially flush with anouter surface of the lead body. In other embodiments, the biasedelectrode is placed in a mold and an electrically insulating material isinjected into the mold to create the lead body. In this manner, thebiased electrode may be integral to the lead body.

Additionally, an electrical conductor is coupled to the biased electrode(94). The conductor extends from a proximal end of the lead body to thebiased electrode and allows a medical device coupled to the proximal endof the lead body to deliver an electrical signal to the biasedelectrode. In one embodiment, the conductor is placed within a lead bodycoupled to the biased electrode. A distal end of the conductor may bewelded or otherwise coupled to the biased electrode. In someembodiments, the electrically insulating lead body includes an aperturethat allows the conductor and biased electrode to make electricalcontact. In embodiments in which the lead body is injection molded, theconductor may be electrically coupled to the biased electrode andpositioned within the mold prior to the injection of the electricallyinsulating material. As this example illustrates, in some embodiments,the conductor may be coupled to the biased electrode before the leadbody is formed and/or before the biased electrode is coupled to the leadbody.

Various examples have been described. However, one of ordinary skill inthe art will appreciate that various modifications may be made to thedescribed examples. For example, although leads in which biasedelectrodes are ring electrodes or otherwise extend substantiallycompletely around the perimeter of the lead have been described herein,a biased electrode may be discontinuous or otherwise extend onlypartially around the perimeter of a lead, but nevertheless have a widththat varies in the longitudinal direction around the perimeter of thelead. As another example, leads used in conjunction with the techniquesdescribed herein may include fixation mechanisms, such as tines thatpassively secure a lead in an implanted position or a helix located at adistal end of the lead that required rotation of the lead duringimplantation to secure the helix to a body tissue. Further, althoughdepicted herein as being located at a distal end of a lead body, inother examples a biased electrode may be located on any portion of alead body. These and other examples are within the scope of thefollowing claims.

The invention claimed is:
 1. An implantable medical lead comprising: alead insulative body; and an electrode pair comprising first and secondelectrodes located along the insulative body, the first electrodelocated proximally to the second electrode, the first and secondelectrodes each having proximal and distal ends, wherein widths of thefirst and second electrodes as measured along a longitudinal directionof the lead vary about a perimeter of the lead; and wherein distancebetween the proximal edge of the first electrode to the distal edge ofthe second electrode is the same around the perimeter of the lead. 2.The lead of claim 1, wherein spacing between the electrodes as measuredalong the longitudinal direction of the lead is substantially constantaround the circumference of the lead.
 3. The lead of claim 2, wherein asum of the width of the first electrode and the width of the secondelectrode is substantially constant around the circumference of thelead.
 4. The lead of claim 1, wherein a sum of the width of the firstelectrode and the width of the second electrode is substantiallyconstant around the circumference of the lead.
 5. A system comprising:an implantable medical lead and a medical device that deliverselectrical stimulation via the lead; wherein the lead comprises: a leadinsulative body; and an electrode pair comprising first and secondelectrodes located along the insulative body, the first electrodelocated proximally to the second electrode, the first and secondelectrodes each having proximal and distal ends, wherein widths of thefirst and second electrodes as measured along a longitudinal directionof the lead vary about a perimeter of the lead; and wherein distancebetween the proximal edge of the first electrode to the distal edge ofthe second electrode is the same around the perimeter of the lead. 6.The system of claim 5, wherein spacing between the electrodes asmeasured along the longitudinal direction of the lead is substantiallyconstant around the circumference of the lead.
 7. The system of claim 6,wherein a sum of the width of the first electrode and the width of thesecond electrode is substantially constant around the circumference ofthe lead.
 8. The system of claim 5, wherein a sum of the width of thefirst electrode and the width of the second electrode is substantiallyconstant around the circumference of the lead.
 9. The system of claim 5,wherein the medical device comprises a cardiac stimulator.
 10. Thesystem of claim 5, wherein the medical device comprises an implantablemedical device.